The present invention relates to methods for molding luminous hollow bodies adapted to be used for signs or the like.
In known methods for manufacturing hollow bodies intended to be used in luminous signs, molds of a given annular or endless configuration are utilized with the contour of such a mold corresponding to the contour of the exterior lateral surface of the hollow body which is to be obtained. Such a mold has applied to its inner surface a suitable number of layers of a synthetic resin composition which is capable of hardening so as to form the side wall of the hollow body of the sign. Then in a subsequent operation the space confined within the thus-molded layers is closed by a suitable base and cap.
With conventional methods of the above type it is possible to achieve for the luminous hollow body an exterior surface of precisely determined configuration having certain characteristics determined by the characteristics of the inner surface of the mold which receives the layers of synthetic resin composition. However, a serious drawback present in such conventional methods resides in the fact that there is no control of the inner surface or even of the wall thickness of hollow bodies manufactured in this way. Thus the nature of the inner surface of such a molded hollow body is completely uncontrolled while at the same time the wall thickness at various parts of the contour of the resulting wall is uncontrolled and in addition there is no control of the regularity of the various layers which form the endless wall. The result of these drawbacks is that there are unavoidable irregularities in the intensity of the illumination provided by the luminous hollow body so that when it is viewed from the exterior with light shining therethrough this light will have an uncontrollable irregularity in the intensity of the illumination at various parts of the hollow body and at the same time there will be undesirable variations in the color or tint. These drawbacks of course appreciably detract from the esthetic appearance of the sign and may even prevent the message which is intended to be given by the sign from being clearly understood.